1. Field of the Invention
The present invention relates to heterogeneous communication systems, and in particular, to a method and a system for transmitting/receiving data in heterogeneous communication systems so that, when a subscriber of the heterogeneous communication systems moves between them, he/she can be seamlessly provided with a service that has been provided to him/her.
2. Description of the Related Art
Much research is being conducted to provide users with services having various levels of Quality of Service (QoS) at high speeds in the next generation communication system. Particularly, considerable study has recently been made with regard to the next generation communication system so as to support high-speed services for a Broadband Wireless Access (BWA) communication system, such as a wireless Local Area Network (WLAN) system or a Wireless Metropolitan Area Network (WMAN) system, which are based on the IEEE (Institute of Electrical and Electronics Engineers) 802.11 standard, while guaranteeing mobility and QoS. Typical examples of such communication systems include an IEEE 802.16a/d communication system and an IEEE 802.16e communication system.
The IEEE 802.16a/d and IEEE 802.16e communication systems, which are BWA communication systems, adopt an Orthogonal Frequency Division Multiplexing (OFDM)/Orthogonal Frequency Division Multiple Access (OFDMA) scheme so as to support a broadband transmission network for the physical channel of the WMAN system. The IEEE 802.16a/d communication system assumes that the Subscriber Station (SS) is currently stationary (i.e. ignores the mobility of the SS) and considers a single cell structure only. In contrast, the IEEE 802.16e communication system considers the mobility of the SS, and the SS having mobility will hereinafter be referred to as a Mobile Station or MS. A conventional IEEE 802.16e communication system will now be described with reference to FIG. 1.
FIG. 1 briefly shows the schematic structure of a conventional IEEE 802.16 communication system.
In FIG. 1, the IEEE 802.16 communication system includes an MS 101; Radio Access Stations (RASs), which are access networks, particularly RASs 1, 2, 3, and 4, numbered 111, 113, 115, and 117, respectively; Access Control Routers (ACRs), particularly ACRs 1 and 2, numbered 121 and 123; an IP (Internet Protocol) network 131; and an Authentication/Authorization/Accounting (AAA) server 141. In the following description, the MS 101 refers to a user or a service subscriber accessing the IEEE 802.16 communication system, or a station used for such access, and the MS 101 is either mobile or stationary.
The RASs 111, 113, 115, and 117 are network equipment for processing specifications regarding wireless connection with the MS 101, which accesses the IEEE 802.16 communication system. The ACRs 121 and 123 are network equipment for performing authentication, Medium Access Control (MAC) protocol processing, IP address allocation, routing, etc. with regard to the MS 101. The IP network 131 provides the MS 101 with an IEEE 802.16 service. The AAA server 141 performs authentication, authorization, and accounting with regard to the MS 101, which has accessed the communication system.
FIG. 2 briefly shows the schematic structure of a conventional IEEE 802.11 communication system.
In FIG. 2, the IEEE 802.11 communication system includes an MS 201; Access Points (APs), particularly APs 1, 2, 3, and 4, numbered 211, 213, 215, and 217, respectively; a Digital Subscriber Line Access Multiplexer/Network Application Support (DSLAM/NAS) 221; a router 223; a switch 225; an IP network 231; a AAA server 241; and a Dynamic Host Configuration Protocol (DHCP) server 243.
The APs 211, 213, 215, and 217 are network equipment for processing specifications regarding wireless connection with the MS 201, which accesses the IEEE 802.11 communication system. The DALAM/NAS 221 and the switch 225 are equipment for controlling the APs 221, 213, 215, and 217. Particularly, the DALAM/NAS 221 uses a Digital Subscriber Line (DSL) so as to provide the MS 201 with an IEEE 802.11 service via the APs 1 and 2, numbered 221 and 223, respectively. The switch 225 uses Ethernet so as to provide the MS 201 with the IEEE 802.11 service via the APs 3 and 4, numbered 215 and 217 respectively.
The router 223 acts as a relay between the DALAM/NAS 221 and the IP network 231 (i.e. conducts routing). The IP network 231 provides the MS 201, which accesses the communication system, with the IEEE 802.11 service. The AAA server 241 performs authentication, authorization, and accounting with regard to the MS 201, which has accessed the communication system, as mentioned above. The DHCP server 243 uses the DHCP so as to allocate an IP address.
FIG. 3 briefly shows a network structure for service interworking between a conventional IEEE 802.16 communication system and an IEEE 802.11 communication system.
In FIG. 3, the network structure for service interworking between the communication systems include RASs for processing specifications regarding wireless connection with an MS 301, which accesses the IEEE 802.16 communication system, particularly RASs 1 and 2, respectively 311 and 313; an ACR 331 for performing authentication, MAC protocol processing, IP address allocation, routing, etc. with regard to the MS 301; APs for processing specifications regarding wireless connection with the MS 301, which accesses the IEEE 802.11 communication system, particularly APs 1 and 2, respectively 321 and 323; an Access Point Controller (APC) 314 for controlling the APs 321 and 323; an IP network 351 for providing the MS 301 with an IEEE 802.16 service and an IEEE 802.11 service; an AAA server 361 for performing authentication, authorization, and accounting with regard to the MS 301, which accesses the IEEE 802.16e and IEEE 802.11 communication systems; and an Home Agent (HA) 371 acting as a router relaying the IEEE 802.16e and IEEE 802.11 communication systems. The APC 323 combines the functions of the DALAM/NAS 221 and the switch 225 described with regard to FIG. 2.
The network for service interworking between the communication systems should provide the MS 301 with IEEE 802.16 and IEEE 802.11 services. As a result, it is necessary to select an optimum wireless access network based on user location (i.e. the location of an MS used in the corresponding system) and service requirements, so that accessing the MSs are provided with voice and data services seamlessly. In short, a scheme for wireless access interworking between heterogeneous systems is requested.
Generally, it is customary to use a mobile IP for interworking between heterogeneous communication systems. For example, the mobile IP is used to support handover when a dual-mode station, which can access both an IEEE 802.16 communication system and an IEEE 802.11 communication system, moves between the heterogeneous communication systems. In this case, not only stations used in respective communication systems, but also every network equipment of the systems (e.g. ACR, APC, etc.) must support the Foreign Agent (FA) function of the mobile IP. In addition, additional network equipment for interworking between the heterogeneous communication systems, such as the HA 371, increases costs and slows down system construction. Furthermore, problems during interworking between the heterogeneous communication systems, particularly signaling delay, triangle routing, and traffic concentration on the HA 371 make it difficult to provide subscribers with efficient services.